MFC r268640 and r268989.

r268640:
Allow multi-byte reads in the private CHELSIO_T4_GET_I2C ioctl.  The
firmware allows up to 48B to be read this way but the driver limits
itself to 8B at a time to remain compatible with old cxgbetool
binaries.

r268989:
Add missing newline to an error message.
MFC	r268985, r269001:
Avoid possible cast degradation.

Assign iov_len first, avoiding the cast to uio_resid
(int in stdio) from degrading the value.

Small cosmetical fix while here.